The present invention relates to reclosable plastic bags and to the lips commonly provided above the closures of such bags for grasping and opening the bags. More particularly, the invention relates to bags of the type disclosed in commonly-assigned U.S. Pat. No. 5,009,828 (the '828 patent) to McCree, wherein "grip strips" are formed on the lips for aiding the consumer in grasping and opening the bags.
In the bags described in the '828 patent, the grip strips on either lip of the bag are comprised of a plurality of small ridges spaced apart in parallel relationship and extending over the width of the bag, with the ridges individually having in one embodiment generally triangular cross-sections. While these bags perform on a par generally with conventional bags not having grip strips on the lips thereof, it has been noted that bags bearing grip strips tend in some instances to have an area of weakness immediately adjacent the lip sidewelds. The lip sidewelds, while satisfactory, could thus be improved.
The present invention arises out of the discovery that by modifying the cross-sectional configuration of the ridges as they are formed, the area of weakness can be eliminated and lip sidewelds of improved strength can result. In this modified cross-section, the ridges have a generally triangular base which is surmounted by a bulbous portion. The bulbous portion provides additional polymer at the tip of the ridge, so that when the tips of the ridges on one sidewall are brought near or into contact with the opposed sidewall in forming the lip sideweld, additional polymer is presented for bonding one lip to another in the area immediately adjacent the sideweld proper. As a result, the overall bond or weld between the lips is strengthened. The present invention is better understood, however, by considering the attached drawings and description.